This article explains how to fix the underlying problem that may result in one or more of the following symptoms:

You have added, rearranged or removed buttons from your toolbar, but the changes are not saved when you restart Firefox.

You have resized or moved the browser window, but the new size and position are not remembered when you restart Firefox.

You cannot save new bookmarks.

Here are two ways that you can solve the problem:

Solution 1: Delete xulstore.json file

You may have a corrupt xulstore.json file in your Firefox profile. You can delete this file so that Firefox can create a new one.

At the top of the Firefox window, click on the Firefox button, go over to the Help menuOn the menu bar, click on the Help menuAt the top of the Firefox window, click on the Help menu and select Troubleshooting Information. The Troubleshooting Information tab will open.Click the menu button
, click help
and select Troubleshooting Information. The Troubleshooting Information tab will open.

Under the Application Basics section, click on Show FolderOpen FolderShow in FinderOpen Directory. A window with your profile filesfolder will open.

At the top of the Firefox window, click on the Firefox button and then select ExitAt the top of the Firefox window, click on the File menu and then select ExitOn the menu bar, click on the Firefox menu and select Quit FirefoxAt the top of the Firefox window, click on the File menu and select Quit.

Click the menu button
and then click ExitQuit
.

Locate and delete the file xulstore.json (or rename it, for example, to xulstore.jsonOLD, to keep the old file as a backup).

You can close the profile folder and open Firefox now.

Solution 2: Refresh Firefox

If you don't want to try the first solution or if it didn't work, the Firefox refresh feature will automatically restore default toolbar settings and browser window size or position, and will also remove add-ons (extensions and themes) that could be interfering.

Note: When using the refresh feature, your bookmarks, browsing history, open tabs, windows, passwords, cookies and web form auto-fill information will be saved. However, your extensions and themes will be removed and your preferences will be reset.When using the reset feature, your bookmarks, browsing history, open tabs, windows, passwords, cookies and web form auto-fill information will be saved. However, your extensions and themes will be removed and your preferences will be reset.When using the reset feature, your bookmarks, browsing history, passwords, cookies and web form auto-fill information will be saved. However, your extensions and themes will be removed; open tabs, windows and tab groups will not be saved; and your preferences will be reset.Learn more.

Click the menu button
and then click help
.

From the Help menu choose Troubleshooting Information.

If you're unable to access the Help menu, type about:support in your address bar to bring up the Troubleshooting Information page.

Click the Refresh Firefox button in the upper-right corner of the Troubleshooting Information page.

To continue, click Refresh Firefox in the confirmation window that opens.

Firefox will close to refresh itself. When finished, a window will list your imported information. Click Finish and Firefox will open.

Note: There's also a Refresh Firefox button in the Firefox Safe Mode window, if you can't start Firefox normally. If you are unable to find the Refresh Firefox button on your version of Firefox, you can also do a manual refresh by creating a new profile. See instructions on how to create a new profile.